Off-stoichiometry effects on crystal nucleation and growth kinetics in soda-lime-silicate glasses. The combeite (Na2O•2CaO•3SiO2) – devitrite (Na2O•3CaO•6SiO2) joint

Abstract

To the present date, the vast majority of fundamental studies on glass crystallization has been carried out using stoichiometric compositions, whereas by far, the most common cases in glass technology are off-stoichiometric. In this work, we performed a comprehensive study on the nucleation and growth kinetics of combeite crystals in non-stoichiometric glasses of the combeite (Na2O•2CaO•3SiO2) – devitrite (Na2O•3CaO•6SiO2) system. Using cluster-size distribution functions based on a previously developed kinetic model of nucleation, we constructed the dependencies of the number N(T) of nucleated and grown crystals on the nucleation time, t, and estimated the nucleation rates, I(T)=dN(T)/dt. We then cross-checked the theoretical calculations versus experimental data. In these calculations, the critical nucleus-supercooled liquid specific interfacial energy, σ, and the effective diffusion coefficient,D, were left as fitting parameters for the best possible description of experimental data. We show that as the precursor glass composition shifts from combeite to devitrite, and thus the difference of composition between the initial glass and the precipitated crystals increases, the interfacial energy increases, and the maximum steady-state nucleation rate, Ist(Tmax), of combeite strongly drops. On the other hand, as a consequence of the composition shift, depending on the glass-forming system, the diffusion coefficient may increase or decrease. We also show a significant difference between D estimated from the nucleation experiments and Du calculated from the growth rates. These results corroborate our previous studies on other systems and are relevant to elucidate the complex mechanisms of crystallization of non-stoichiometric glasses.